What does a solid line indicate in vehicle maintenance documentation?

In vehicle maintenance documentation, a solid line specifically indicates that the information pertains only to one side of the vehicle. This is crucial for ensuring accurate maintenance and repairs, as different sides of a vehicle can have distinct components or requirements. Understanding this distinction helps maintenance personnel effectively carry out their tasks without confusion regarding which side of the vehicle the documentation is referring to.

In contrast, the other options do not accurately reflect the significance of a solid line. For instance, a solid line does not convey that the information is applicable to both sides, nor does it indicate mandatory actions or optional equipment. Therefore, the clarity provided by a solid line is vital for the correct interpretation of vehicle maintenance instructions.